1. Field of the Invention
The present invention relates generally to a cold cathode fluorescent lamp drive apparatus and particularly to a cold cathode fluorescent lamp drive apparatus for lighting a cold cathode fluorescent lamp.
2. Description of the Related Art
In recent years and continuing, a liquid crystal display (LCD) panel is being widely used as a monitor of a television or a personal computer owing to its thin structure and low energy consumption. It is noted that the liquid crystal display panel itself is not provided with a light emitting function, and thereby, display is realized at the liquid crystal display panel by transmitting or reflecting natural light or light from a lighting system such as a backlight or a front light, for example. A cold cathode fluorescent lamp (CCFL) may be used in a lighting system for a liquid crystal display panel.
Owing to the characteristics of the cold cathode fluorescent lamp, a voltage of around a dozen hundred volts needs to be applied upon initially lighting the cold cathode fluorescent lamp, and a voltage of several hundred volts needs to be applied after lighting the cold cathode fluorescent lamp.
FIG. 1 is a block diagram showing a configuration of an exemplary lighting system using a cold cathode fluorescent lamp according to the prior art.
The lighting system 1 shown in FIG. 1 includes a cold cathode fluorescent lamp unit 11, a power source circuit 12, a current detection circuit 13, and a protection circuit 14.
In this system, a drive voltage from the power source circuit 12 is applied to the cold cathode fluorescent lamp unit 11. An input voltage Vin is applied to an input terminal Tin of the power source circuit 12. The power source circuit 12 is arranged to increase the input voltage Vin input to the input terminal Tin and apply the increased voltage to one end of the cold cathode fluorescent lamp unit 11.
The other end of the cold cathode fluorescent lamp unit 11 is grounded via the detection circuit 13. The detection circuit 13 converts a current flowing in the cold cathode fluorescent lamp unit 11 into a voltage and supplies the converted voltage to the protection circuit 14.
The protection circuit 14 includes a current control circuit 21, a lighting failure detection circuit 22, and a forced shutdown circuit 23.
The voltage converted by the current detection circuit 13 according to the current flowing in the cold cathode fluorescent lamp unit 11 is supplied to the current control circuit 21. The current control circuit 21 is arranged to control the voltage being applied to the cold cathode fluorescent lamp unit 11 from the power source circuit 12 according to the voltage supplied from the current detection circuit 13 so that the current flowing in the cold cathode fluorescent lamp unit 11 may be maintained at a fixed level.
The voltage converted by the current detection circuit 13 according to the current flowing in the cold cathode fluorescent lamp unit 11 is also supplied to the lighting failure detection circuit 22. The lighting failure detection circuit 22 is arranged to detect a lighting failure of the cold cathode fluorescent lamp unit 11 according to the voltage supplied from the detection circuit 13. A detection signal generated at the lighting failure detection circuit 22 is supplied to the forced shutdown circuit 23. When the detection signal from the lighting failure detection circuit 22 indicates a lighting failure detection state, the forced shutdown circuit 23 temporarily shuts down the operation of the power source circuit 12.
In Japanese Laid-Open Patent Publication No. 3-112092, technology is disclosed for improving the response speed of a protective function of a fluorescent lamp lighting system for protecting a fluorescent lamp used therein by providing a detection circuit that is arranged to detect a current flowing in the fluorescent lamp to detect an abnormality of the fluorescent lamp.
In Japanese Laid-Open Patent Publication No. 2002-141186, technology is disclosed for protecting a fluorescent lamp used in a fluorescent lamp lighting system by providing a detection circuit that detects a current flowing in the fluorescent lamp to detect an abnormality of the fluorescent lamp and shuts down the operation of a power source circuit that supplies a power voltage to the fluorescent lamp when an abnormality is detected.
It is noted that the cold cathode fluorescent lamp unit 11 is connected to the power source circuit 12 and the current detection circuit 13 via connectors CN. When a small gap is formed at a connection point due to malconnection of the connector CN, electrical discharge such as arcing may occur. In this case, the electrical discharge caused by the malconnection of the connector CN may continually occur from vibration, for example, unless measures are taken to fix the connection of the connector CN.
In the cold cathode fluorescent lamp drive system according to the prior art, a current flowing in cold cathode fluorescent lamp unit 11 is detected in order to detect an abnormality of the cold cathode fluorescent lamp unit 11, and the protective function of the system is operated only when an abnormality is detected. Thereby, even when electrical discharge such as arcing occurs from receiving a high voltage due to malconnection of the connector CN, when a connection state is reestablished, the protective action may be lifted, and a high voltage may be applied to the fluorescent lamp once more to cause the occurrence of the electrical discharge. That is, the system may be continually used even in an abnormal state, and thereby, problems may occur with respect to stability and reliability of the system operation.